1. Field of the Invention:
This invention relates generally to solid-state circuit interrupters and more specifically, to such circuit interrupters as are utilized in molded case and metal clad type circuit interrupters and as are capable of acting on a number of complex electrical parameters in order to protect the electrical conducting system and devices connected thereto. This invention further relates to such circuit interrupters that allow for system user interaction so that the number of electrical parameters can be easily and readily understood and responded to.
2. Description of the Prior Art:
The solid-state circuit interrupter is being employed today for significantly more complex commercial and industrial applications than was the original circuit interrupter first introduced as a resettable replacement for a common fusing element. Additionally, with the recent explosion in the use and performance attributes of the microprocessor arts along with the coincident increasing cost advantage for such devices, the application of microprocessor teachings to the circuit interrupter field has brought a commensurate demand for more complex analysis, greater performance features, and easier interaction with the solid-state circuit interrupter while at the same time, maintaining or improving the cost factor for such circuit interrupters.
An existing microprocessor based solid-state circuit interrupter is disclosed in U.S. Pat. No. 4,331,997 issued to Engel and assigned to the same assignee as the present application. This device was able to apply microprocessor technology to existing circuit interrupters while maintaining the supervisory control over such factors as instantaneous protection, short delay protection, long delay protection and ground fault protection that were found on existing solid-state circuit interrupters such as those that utilized discrete or other integrated circuit electronic components. As examples of circuit interrupters utilizing discrete components, reference is now made to U.S. Pat. No. 3,590,326 issued to Watson on June 29, 1971 and U.S. Pat. No. 3,818,275 issued to Shimp on June 18, 1974. In addition, the microprocessor based circuit interrupter was able to incorporate display and input monitoring techniques that provided for more accurate and reliable interface and operation of the electrical distribution system on which the circuit interrupter was being utilized.
This processor based circuit interrupter also proved advantageous in energy management systems where it was necessary to configure the electrical distribution system to achieve maximum energy efficiency and a minimum circuit interruption to the system as a whole. It is well known in the field that in configuring an electrical distribution system, a main circuit interrupter which protects a line feeding a number of branch circuits each having a branch circuit interrupter disposed thereon, should have delay times assigned so that in the event of a fault in one of the branch circuits, the associated branch circuit interrupter would trip before the main circuit interrupter. In this manner, the entire electrical distribution system would not be interrupted by a fault condition in a branch circuit and, the device or devices which that branch circuit was feeding, would also be protected in a more timely manner. Still other zone interlocking conditions can be accommodated using similar design criteria as the above example.
The microprocessor based circuit interrupter also proved advantageous over existing circuit interrupters in the method of selecting and adjusting the tripping parameters. The electrical distribution system design was greatly simplified since it was no longer required that a trial-and-error approach to field timing the tripping parameters be performed.
This microprocessor based circuit interrupter though effective and certainly an advance over the then existing circuit interrupters, did have certain limitations that the present application addresses and overcomes. For instance, it would have been a great advantage to have a communication link tied to the microprocessor based circuit interrupter so that in working with an energy management system the circuit interrupter could be instructed from a remote location to perform various supervisor tasks such as, for example, a load shedding operation.
Another example of such a limitation can be found in the use of what is typically referred to as the rating plug. The rating plug serves to establish at least one of the current limiting factors for the circuit interrupter, these current limiting factors being the frame rating factor which establishes the maximum current flow through the particular circuit interrupter, and the plug rating factor which establishes the selected maximum current flow for the particular application of this circuit interrupter. It is commonly the practice though that the plug rating factor can be one of a number of stepped down factors relative to the frame rating factor; that is, the plug rating factor can be any one of a number of possible values lower in magnitude than the frame rating factor.
It is also a requirement that in selecting the plug rating factor, a limit as to the amount of ground current permissible in a ground path associated with the electrical conducting circuit, be selected as well. Unlike the selection of the plug rating value though, the selection of the ground current limit must be made in view of certain standard specifications, as for instance, the UL and NEC Standards. As such, the circuit interrupter of the past has been required to include a rating plug that not only allowed for the selection of the variety of plug rating factors, but in addition, provided for a variety of selections for the ground current limit which were not in excess of the standard specifications.
The possible combinations of plug rating factors and ground fault limits made the task of stocking sufficient inventory a monumental one and, where attempts were made to minimize inventory stocking requirements, it was done so using various hardware techniques. As an example, a mechanical blocking bracket was used in conjunction with a range selecting potentiometer whereby the bracket prevented the selecting of ground fault current limits in excess of the standard specifications.
Another method used was to change various level resistors on a printed circuit board with the excess limit settings being masked off the board so that only the safe selection of the ground fault current limit could be made. This approach however, further required additional inventory and manufacturing operations to achieve the various desired level settings.